Ocean Acidification & Climate Change

The deep-sea was originally thought to be buffered against the effect of surface-driven cycles. Now, modern research suggests otherwise. Global changes in surface productivity and environmental variables such as temperature or salinity could potentially influence deep sea species’ distribution, abundance and behaviour (Levin et al. 2001, Ruhl & Smith 2004).

Levels of atmospheric CO2 are increasing rapidly and certain modeled scenarios show that this will lead to the highest increase of ocean acidification in the last 300 million years (Caldeira & Wickett 2003). If atmospheric CO2 doubled tropical coral calcification would be reduced by 54%. It is unknown what affect this would have on CWCs but given the lower saturation rate of Calcium carbonate at higher latitudes and deeper waters that would occur, they definitely will be more vulnerable (Guinotte et al. 2006).  Ocean acidification would also lead to a shallowing of the ASH by several hundred meters (figure 11), resulting in under-saturated deep waters that will be unable to sustain reef building stony corals.

Four graphs showing shallowing of Aragonite saturation horizon in future years to come

Fig.11.(a) Projected ASH depth for 1765, (b) year 2020, (c) year 2060 (d) year 2099. (adapted from Guinotte et al. 2006).

Increased temperatures will have a negative effect on corals’ food supply as well. Surface productivity, especially in phytoplankton, has been strongly linked with climatic fluctuations. 2-4% of surface spring-blooms reach the sea floor in the North-east Atlantic providing an important food source for CWCs. However with increased blooms comes an increase in the number of grazers (Freiwald et al. 2004), ¬†such as formaniferans, meaning that less food will circulate to deep-waters below. Not only that but when the formaniferans die there will be a greater amount of shell debris on the sea floor disrupting reefs. Smith & Kaufmann (1999) noted that in the North Pacific, declines in food supply from surface waters led to a decrease in community oxygen consumption. These surface disturbances are likely to alter the species distributions seen in the deep.

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